2.1 Interferons:
Type I interferons (IFN) (IFNα, IFNβ, IFNω, IFN-τ) are a family of structurally related cytokines having antiviral, antitumor and immunomodulatory effects (Hardy et al. (2001) Blood 97:473; Cutrone and Langer (2001) J. Biol. Chem. 276:17140). The human IFNα locus includes two subfamilies. The first subfamily consists of 14 non-allelic genes and 4 pseudogenes having at least 80% homology. The second subfamily, αII or omega (ω), contains 5 pseudogenes and 1 functional gene which exhibits 70% homology with the IFNα genes (Weissmann and Weber (1986) Prog. Nucl. Acid Res. Mol. Biol., 33:251-300). The subtypes of IFNα have different specific activities but they possess the same biological spectrum (Streuli et al. (1981) Proc. Natl. Acad. Sci. USA 78:2848) and have the same cellular receptor (Agnet M. et al. in “Interferon 5” Ed. I. Gresser p. 1-22, Academic Press, London 1983). Interferon alpha subtypes have been identified with the following nomenclature: IFNα 1, 2a, 2b, 4, 4b, 5, 6, 7, 8, 10, 14, 16, 17, and 21.
The interferon β (IFNβ) is encoded by a single gene, which has approximately 50% homology with the IFNα genes.
Interferon γ, which is produced by activated lymphocytes, does not possess any homology with the alpha/beta interferons and it does not react with their receptor.
2.1.1 Interferon Receptors:
All human type 1 interferons bind to a cell surface receptor (IFN alpha receptor, IFNAR) consisting of two transmembrane proteins, IFNAR1 and IFNAR2 (Uze et. al. (1990) Cell 60:225; Novick et al. (1994) Cell 77:391). IFNAR1 is essential for high affinity binding and differential specificity of the IFNAR complex (Cutrone et al. 2001 J. Bio Chem 276(20):17140-8) While functional differences for each of the type I IFN subtypes have not been identified, it is thought that each may exhibit different interactions with the IFNAR receptor components leading to potentially diverse signaling outcomes (Cook et al. (1996) J. Biol. Chem. 271:13448). In particular, studies utilizing mutant forms of IFNAR1 and IFNAR2 suggested that alpha and beta interferons signal differently through the receptor by interacting differentially with respective chains (Lewerenz et al. (1998) J. Mol. Biol. 282:585).
2.1.2 Function of Interferons:
Early functional studies of type I IFNs focused on innate defense against viral infections (Haller et al. (1981) J. Exp. Med. 154:199; Lindenmann et al. (1981) Methods Enzymol. 78:181). More recent studies, however, implicate type I IFNs as potent immunoregulatory cytokines in the adaptive immune response. Specifically, type I IFNs have been shown to facilitate differentiation of naïve T cells along the Th1 pathway (Brinkmann et al. (1993) J. Exp. Med. 178:1655), to enhance antibody production (Finkelman et al. (1991) J. Exp. Med. 174:1179) and to support the functional activity and survival of memory T cells (Santini et al. (2000) J. Exp. Med. 191:1777; Tough et al. (1996) Science 272:1947).
Recent work by a number of groups suggests that IFNα may enhance the maturation or activation of dendritic cells (DCs) (Santini, et al. (2000) J. Exp. Med. 191:1777; Luft et al. (1998) J. Immunol. 161:1947; Luft et al. (2002) Int. Immunol. 14:367; Radvanyi et al. (1999) Scand. J. Immunol. 50:499). Furthermore, increased expression of type I interferons has been described in numerous autoimmune diseases (Foulis et al. (1987) Lancet 2:1423; Hooks et al. (1982) Arthritis Rheum. 25:396; Hertzog et al. (1988) Clin. Immunol. Immunopathol. 48:192; Hopkins and Meager (1988) Clin. Exp. Immunol. 73:88; Arvin and Miller (1984) Arthritis Rheum. 27:582). The most studied examples of this are insulin-dependent diabetes mellitus (IDDM) (Foulis (1987)) and systemic lupus erythematosus (SLE) (Hooks (1982)), which are associated with elevated levels of IFNα, and rheumatoid arthritis (RA) (Hertzog (1988), Hopkins and Meager (1988), Arvin and Miller (1984)), in which IFNβ may play a more significant role.
Moreover, administration of interferon α has been reported to exacerbate underlying disease in patients with psoriasis and multiple sclerosis and to induce an SLE like syndrome in patients without a previous history of autoimmune disease. Interferon α has also been shown to induce glomerulonephritis in normal mice and to accelerate the onset of the spontaneous autoimmune disease of NZB/W mice. Further, IFNα therapy has been shown in some cases to lead to undesired side effects, including fever and neurological disorders. Hence there are pathological situations in which inhibition of Type I IFN activity may be beneficial to the patient and a need exists for agents effective in inhibiting Type I IFN activity.
2.1.3 Antibody Effector Functions:
The Fc region of an antibody interacts with a number of ligands (also referred herein as “Fc ligands” which include but are not limited to agents that specifically bind to the Fc region of antibodies, such as Fc receptors and C1q) including Fc receptors and C1q, imparting an array of important functional capabilities referred to as effector functions. The Fc receptors mediate communication between antibodies and the cellular arm of the immune system (Raghavan et al., 1996, Annu Rev Cell Dev Biol 12:181-220; Ravetch et al., 2001, Annu Rev Immunol 19:275-290). In humans this protein family includes FcγRI (CD64), including isoforms FcγRIA, FcγRIB, and FcγRIC; FcγRII (CD32), including isoforms FcγRIIA, FcγRIIB, and FcγRIIC; and FcγRIII (CD16), including isoforms FcγRIIIA and FcγRIIB (Jefferis et al., 2002, Immunol Lett 82:57-65). These receptors typically have an extracellular domain that mediates binding to Fc, a membrane spanning region, and an intracellular domain that may mediate some signaling event within the cell. These receptors are expressed in a variety of immune cells including monocytes, macrophages, neutrophils, dendritic cells, eosinophils, mast cells, platelets, B cells, large granular lymphocytes, Langerhans' cells, natural killer (NK) cells, and T cells. Formation of the Fc/FcγR complex recruits these effector cells to sites of bound antigen, typically resulting in signaling events within the cells and important subsequent immune responses such as release of inflammation mediators, B cell activation, endocytosis, phagocytosis, and cytotoxic attack. The ability to mediate cytotoxic and phagocytic effector functions is a potential mechanism by which antibodies destroy targeted cells. The cell-mediated reaction wherein nonspecific cytotoxic cells that express FcγRs recognize bound antibody on a target cell and subsequently cause lysis of the target cell is referred to as antibody dependent cell-mediated cytotoxicity (ADCC) (Raghavan et al., 1996, Annu Rev Cell Dev Biol 12:181-220; Ghetie et al., 2000, Annu Rev Immunol 18:739-766; Ravetch et al., 2001, Annu Rev Immunol 19:275-290). The cell-mediated reaction wherein nonspecific cytotoxic cells that express FcγRs recognize bound antibody on a target cell and subsequently cause phagocytosis of the target cell is referred to as antibody dependent cell-mediated phagocytosis (ADCP). In addition, an overlapping site on the Fc region of the molecule also controls the activation of a cell independent cytotoxic function mediated by complement, otherwise known as complement dependent cytotoxicity (CDC).
2.1.4 The Different Types of Human FcγR:
Human FcγRs are divided into three distinct classes: FcγRI (CD64), FcγRII (CD32) and FcγRIII (CD16). FcγRI is a high affinity receptor (Ka: 10−8-10−9 M−1) and binds both immune complexes and monomeric IgG molecules while the Fc receptors FcγRII and FcγRIII exhibit lower affinities (<10−7 M−1 and 2-3×10−7 respectively) (Gessner J. E. et al., 1998, Annn Hematology 76:231-48). Signaling through the FcγRs is either through an immunoreceptor tyrosine-based activation motif (ITAM) or immunoreceptor tyrosine-based inhibitory motif (ITIM) for all the transmembrane receptors (Presta 2006, Adv Drug Deli Rev 58:640-656).
The 72 kDa extracellular glycoprotein FcγRI is mainly expressed on myeloid cells such as monocytes, macrophages CD4+ progenitor cells and may elicit the ADCC, endocytosis, and phagocytosis responses (Siberil et al. 2006, J Immunol Lett 106:111-118).
The 40 kDa FcγRII group of receptors (A, B and C isoforms) exhibit extracellular domains but do not contain active signal transduction domains. These receptors propagate signals through phosphorylation of a cytoplasmic tail domain (Amigorena S. et al., 1992 Science. 256:1808-12). The FcγRIIA is mainly expressed on monocytes, macrophages, neutrophils, and platelets whereas the FcγRIIC receptor has only been identified on NK cells. These two receptors have been shown to initiate ADCC, endocytosis, phagocytosis and inflammatory mediator release (Cassel et al. 1993. Mol Immunol 30:451-60). By contrast, the FcγRIIB (B1 and B2 types) receptors are expressed on B cells, Mast cells, basophils, monocytes, macrophages and dendritic cells and has been shown to downregulate the immune response triggered by the A and C isoforms.
The 50 kDa FcγRIIIA, expressed on NK cells, monocytes, macrophages and a subset of T lymphocytes where it activates ADCC, phagocytosis, endocytosis and cytokine release (Gessner et al.). The FcγRIIIB isoforms is a glycosyl-phosphatidylinositol (GPI) anchored peripheral membrane protein involved in the degranulation and the production of reactive oxygen intermediates (Salmon J. E. et al. 1995 J Clin Inves 95:2877-85).
IgG molecules also exhibit differential isotype specificity for FcγRs. IgG3 molecules bind strongly to all FcγR isoforms. IgG1, the most prevalent isoforms in the blood binds to all FcγRs albeit with a lower affinity for the FcγRIIA/B isoforms. IgG4 is an intermediate binder to FcγR1 and a weak binder to FcγRIIB. Finally, IgG2 binds only weakly to one allelic form of FcγRIIA (FcγRIIA-H131) (Siberil et al. 2006, J Immunol Lett 106:111-118).
2.1.5 Complement
The complement inflammatory cascade is a part of the innate immune response and is crucial to the ability for an individual to ward off infection. Another important Fc ligand is the complement protein C1q. Fc binding to C1q mediates a process called complement dependent cytotoxicity (CDC) (reviewed in Ward et al., 1995, Ther Immunol 2:77-94). C1q is capable of binding six antibodies, although binding to two IgGs is sufficient to activate the complement cascade. C1q forms a complex with the C1r and C1s serine proteases to form the C1 complex of the complement pathway.
2.1.6 Regions and Amino-acid Residues of IgG Involved in FcγR Binding
The mapping of human IgG binding sites to different FcγR has been studied extensively. These studies, based on genetically altered IgG molecules have identified a short continuous stretch of amino acid residues (234-238) of the N-terminus part of the CH2 domain as being directly involved in the binding to all FcγRs. Additionally, residues 268, 297, 327 and 329 may impact binding to a subset of FcγRs. Also, multiple residues located in the CH2 and CH3 domains also contribute to FcγR binding (Canfield S M. et al., 1991 J Exp Med 173:1483-91, Chappel M S. Et al. 1991, Proc Nat Acad Sci USA 888:9036-40, Gergely J. et al. 1990 FASEB J 4:3275-83).
2.2 Antibody Therapeutic Related Toxicity
In many circumstances, the binding and stimulation of effector functions mediated by the Fc region of immunoglobulins is highly beneficial, however, in certain instances it may be more advantageous to decrease or eliminate effector function. This is particularly true for those antibodies designed to deliver a drug (e.g., toxins and isotopes) to the target cell where the Fc/FcγR mediated effector functions bring healthy immune cells into the proximity of the deadly payload, resulting in depletion of normal lymphoid tissue along with the target cells (Hutchins et al., 1995, PNAS USA 92:11980-11984; White et al., 2001, Annu Rev Med 52:125-145). In these cases the use of antibodies that poorly recruit complement or effector cells would be of tremendous benefit (see for example, Wu et al., 2000, Cell Immunol 200:16-26; Shields et al., 2001, J. Biol Chem 276:6591-6604; U.S. Pat. Nos. 6,194,551; 5,885,573 and PCT publication WO 04/029207).
In other instances, for example, where blocking the interaction of a widely expressed receptor with its cognate ligand is the objective, it would be advantageous to decrease or eliminate all antibody effector function to reduce unwanted toxicity. Also, in the instance where a therapeutic antibody exhibited promiscuous binding across a number of human tissues it would be prudent to limit the targeting of effector function to a diverse set of tissues to limit toxicity. Although there are certain subclasses of human immunoglobulins that lack specific effector functions, there are no known naturally occurring immunoglobulins that lack all effector functions. An alternate approach would be to engineer or mutate the critical residues in the Fc region that are responsible for effector function. For examples see PCT publications WO2006076594, WO199958572, US20060134709, WO2006047350, WO2006053301, and U.S. Pat. No. 5,624,821 each of which are incorporated by reference in their entireties.
The use of monoclonal antibodies in the treatment of many disease states has been well documented. With the myriad of effector functions that an antibody can trigger, one of the requirements of antibody therapeutics is that they are targeted specifically to a target of interest. For example, but not limited to, the specificity of a target tissue is analyzed by examining the immunohistochemistry (IHC) of a tissue of interest. It is important that the therapeutic only bind to tissues that contain a target of interest. Failure to do so could result in higher toxicity of the antibody therapeutic due to inappropriate activation of effector function elicited at the non-targeted site. If the effector function could be diminished or ablated, the danger of the widespread binding of the therapeutic could be avoided. With all these considerations, there is an unmet need for antibodies with reduced or ablated affinity for at least one Fc ligand responsible for facilitating effector function. Such antibodies would be of particular benefit for use in the treatment of chronic inflammatory and autoimmune conditions.
Citation or discussion of a reference herein shall not be construed as an admission that such is prior art to the present invention.